ADONET64 vertica driver returns empty DataTable on Select count(*)
joergschaber
Vertica Customer ✭
Hi,
sometimes my ADONET64 vertica driver returns an empty DataTable, when I run a "Select count(*) from " a View.
The c# code is the following:
VerticaCommand command = _dbConnection.CreateCommand();
command.Connection = _dbConnection;
command.CommandText = "SELECT COUNT(*) FROM View";
// Create the DataAdapter
VerticaDataAdapter adapter = new VerticaDataAdapter {SelectCommand = command};
// Fill the DataTable
DataTable result = new DataTable();
adapter.Fill(result);
After adapter.Fill(result) result should be a data table with one row, but sometimes it is just empty.
Any idea? Is that a bug in the driver?
vertica and driver version is v10.0.1-6
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Best Answer
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joergschaber
Vertica Customer ✭
I think we found the problem. We figured that we probably had parallel queries using a async methods running the queries.
Thanks.0
Answers
Can you check to see if the query is reaching Vertica?
To do that, query the SYSTEMS tables.
Example...
verticademos=> CREATE VIEW d_view AS SELECT * FROM dual; CREATE VIEW verticademos=> \! vsql -c "SELECT COUNT(*) FROM d_view;" COUNT ------- 1 (1 row) verticademos=> SELECT user_name, transaction_id, statement_id, success FROM query_requests WHERE request = 'SELECT COUNT(*) FROM d_view;';z user_name | transaction_id | statement_id | success -----------+-------------------+--------------+--------- dbadmin | 45035996274039952 | 1 | t (1 row) verticademos=> SELECT session_id, transaction_id, statement_id, processed_row_count FROM query_profiles WHERE query = 'SELECT COUNT(*) FROM d_view;'; session_id | transaction_id | statement_id | processed_row_count --------------------------------------+-------------------+--------------+--------------------- erticademos_node0001-1145916:0x97e5a | 45035996274039952 | 1 | 1 (1 row)Are there times whene the SUCCESS flag is false?
If so, take a peek at the DC_ERRORS Data Collector table for the related TRANSACTION_ID and STATEMENT_ID:
SELECT log_message FROM dc_errors WHERE transaction_id = 45035996274039952 AND statement_id = 1;Hi,
yes, we checked and it seems that queries are not reaching Vertica and there are no queries with success = false.
This errors seems to occur, when we query data sets where count = 0 and/or we have several queries in a milliseconds time interval.